"Their blood has wash'd out their foul footstep's pollution.
No refuge could save the hireling and slave
From the terror of flight or the gloom of the grave,
And the star-spangled banner in triumph doth wave
O'er the land of the free and the home of the brave."
The mere mention of "slave" is not entirely remarkable; slavery was alive and well in the United States in 1814. Key himself owned slaves, was an anti-abolitionist and once called his African brethren "a distinct and inferior race of people."
Some interpretations of these lyrics contend Key was in fact taking pleasure in the deaths of freed black slaves who had decided to fight with the British against the United States.
In order to bolster their numbers, British forces offered slaves their freedom in British territories if they would join their cause during the war. These black recruits formed the Colonial Marines, and were looked down upon by people like Key who saw their actions as treasonous.